TfL is reminding drivers that vehicles more than two metres (six foot six inches) wide are not permitted through the Rotherhithe Tunnel.
The tunnel, which opened in 1908, was never designed to carry the type of traffic that it does today. Soon after opening in 1908, the Rotherhithe Tunnel was moving 2,600 vehicles, mainly horse-drawn. This has now grown by more than ten times to 30,000 modern vehicles
As a result wide vehicles, generally vans or bigger, were banned from the tunnel in 2012.
TfL claim removing these vehicles from the tunnel reduces the risk of collisions, which have the potential to cause serious injuries to drivers and cause significant congestion in the surrounding area.
Glynn Barton, TfL's Director of Network Management, said: 'These restrictions are in place for very important reasons.
'This tunnel is more than a century old and was not designed for these types of vehicle so vans and wider vehicles risk colliding inside it, increasing road danger and disruption in the area.'
'We brought these restrictions in six years ago and we are reminding Londoners that they are there and why they are so important.'
As part of its regular monitoring of its network, TfL has identified that up to 6,500 vehicles wider than the restrictions could be illegally entering the tunnel every day, despite the clear signage on all approaches highlighting the restrictions.
Vehicles that use the tunnel illegally risk receiving a fine of £50 or prosecution.
Drivers restricted from the Rotherhithe Tunnel should use Tower Bridge or the Blackwall Tunnel - both of which are outside of the Congestion Charge.